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Objective To investigate whether high estimates of the burden of depression could be attributed to an overestimation of disability weights (reflecting more severe disability). Methods We derived disability weights that were tailored to prevalence data. Empirical disability data from a Dutch community survey was used to describe three classes of severity of depression and their proportional prevalence. We obtained valuations from experts for each class and calculated the overall disability weight for depression. Findings Expert valuations were similar to those of previous studies. The overall disability weight for depression was similar to other studies except the 1994 Dutch Burden of Disease Calculation, which it exceeded by 73%. The lower Dutch 1994 disability weight resulted from an overestimation of the proportion of mild cases of depression by experts (60% versus 27% observed in the empirical data used in the present study). Conclusion This study found no indication that disability associated with depression was overestimated. The Dutch example showed the importance of tailoring disability weights to epidemiological data on prevalence.
Keywords Depressive disorder, Major; Disability evaluation; Disabled persons/statistics; Cost of illness; Comparative study; Netherlands (source: MeSH, NLM).
Mots clés Dépression involutive; Evaluation incapacité; Handicapé/statistique; Coût maladie; Etude comparative; Pays-Bas (source: MeSH, INSERM).
Palabras clave Depresión involutiva; Evaluación de la incapacidad; Personas incapacitadas/estadística; Costo de la enfermedad; Estudio comparativo; Países Bajos (fuente: DeCS, BIREME).
Bulletin of the World Health Organization 2005;83:443-448.
Voir page 446 le résumé en français. En la página 447 figura un resumen en español.
Has the burden of depression been overestimated? Michelle E. Kruijshaar,1 Nancy Hoeymans,2 Jan Spijker,3 Marlies E.A. Stouthard,4 & Marie-Louise Essink-Bot1
1 Department of Public Health, Erasmus MC, University Medical Center Rotterdam, PO Box 1738, 3000 DR Rotterdam, the Netherlands. Correspondence should be sent to Dr Kruijshaar at this address (email: m.kruijshaar@erasmusmc.nl). 2 Department for Public Health Forecasting, National Institute of Public Health and the Environment, Bilthoven, the Netherlands. 3 The Netherlands Institute of Mental Health and Addiction, Utrecht, the Netherlands. 4 Academic Medical Centre, University of Amsterdam, the Netherlands. Ref No. 04-013086 (Submitted: 11 March 2004 – Final revised version received: 17 November 2004 – Accepted: 18 November 2004)
Introduction One of the major findings of the 1990 global burden of disease study was the importance of major depression as a contributor to the worldwide disease burden, with an impact exceeding that of cerebrovascular disease and cancers (1). The measure of the burden of disease used in this study, the disability-adjusted life year, combines the number of life-years lost due to premature mortality and the number of years lived with disability using a set of disease-specific disability weights. Years lived with depres- sion were weighted for the severity of the disability associated with the disease using depression-specific disability weights. The prominence of major depression as a contributor to disease burden was replicated in several national burden of disease studies that followed the 1990 study (2–4) and in the 2000 study (5). This high burden is based on the high prevalence figures for major depression found in community surveys (6–8) and the high disability weights derived from expert opinion. Although the effects of major depression on functioning and well-being are reported to be strong (8–12), the high disability weights used in burden-of-disease studies may be questioned
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because much of the empirical information on disability from depression comes from clinical cases. Population surveys, on the other hand, may include milder cases of depression than those found in clinical settings (13). Because prevalence estimates are derived from general population surveys, the disability weights may, consequently, be too high. The burden of major depres- sion relies heavily on these estimates, as the mortality compo- nent is low (1–5).
The aim of our study was to investigate whether the burden of depression has been overestimated because disability weights have been inaccurately tailored to the prevalence data. We used information on disability taken from a community survey as reported by people with depression. Disability was defined as limitations in the physical, psychological and social domains of functioning. Previously, we distinguished three clus- ters of severity of major depression: mild, moderate to severe, and severe with psychotic features (14). We derived empirical disability weights for these three classes of severity and com- bined them with their empirical prevalence estimates into an overall disability weight for major depression.
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Box 1. Example of disease-stage description for depression
Depression Depression is divided into the following stages: 1. mild 2. moderate to severe 3. severe with psychotic features.
We now ask you to value:
Patients with moderate to severe depression These people experience one or more depressive episodes within a year. During these periods they go through permanent feelings of sadness or emptiness and a permanent loss of interest or pleasure in nearly all activities. They have problems eating and/or sleeping and feel worthless or guilty. They may have thoughts of death.
In a year in which one or more episodes are experienced, their condition is such that they have:
• no problems in walking about • no problems with self-care • some problems with performing usual activities (e.g. work, study,
housework, family or leisure activities) • moderate pain or discomfort (feeling tired) • moderate anxiety or depression • some cognitive impairments (with memory, concentration, disorga-
nization, IQ level)
Methods The study was divided into four parts: 1. a valuation study to derive disability weights for the three
classes of severity; 2. a comparison of the results with a previous valuation study; 3. the calculation of an overall disability weight for major
depression; 4. comparison of the overall disability weight to previous
estimates of disability weights for major depression.
Valuation study Disease selection, staging and description We included four other disorders in the valuation study to pre- vent bias. The disorders we asked experts to value were: major depression, obsessive–compulsive disorder, oesophageal cancer, prostate cancer, and vision disorders. Each disease was subdi- vided into different stages that were assumed to represent a homogeneous group of people in terms of disability, treatment and prognosis. In total 18 disease-stages were valued: the three severity classes of major depression, three stages for oesophageal cancer, two for obsessive–compulsive disorder, and five for each of the other two disorders.
A lay-accessible version of the text and a standardized functional health status description were provided for each disease stage. An example of the lay text and the standardized functional health status description are shown in Box 1. We used a health classification system adapted from the original EuroQol 5D-3L classification and refer to it as EuroQol 5D+C5L (15, 16). It includes cognition as a sixth dimension of health (5D+C) along with mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. We have adapted the three levels to a five-level scale (5L): in this scheme the first, third and fifth levels are identical to those in EuroQol 5D-3L but we have added two intermediate levels.
For major depression we based the information in the lay text on the criteria for major depression and its severity as defined by the Diagnostic and statistical manual of mental disorders, third edition, revised (DSM-III-R). The EuroQol description was based on data from the Netherlands Mental Health Survey and Incidence Study (NEMESIS) (9, 14). The eight scales of the Short Form-36 health survey (17) were used as indicators of disability along with two additional questions. These questions asked about the number of days spent in bed due to psychiatric problems, drug-related problems or alcohol- related problems, and the number of days someone was unable to work due to these problems. We used a formal algorithm (available from the authors on request) to map these disability data onto the EuroQoL 5D+C5L classification.
For comparative purposes, the descriptions of obsessive– compulsive disorder and oesophageal cancer were the same as those used in a previous study, the Dutch disability weights study (18). We re-coded the associated EuroQol 5D+C3L descriptions into the 5D+C5L instrument. Descriptions and resulting values for prostate cancer and vision disorders will be presented elsewhere.
Valuation procedure and respondents The valuation procedure was largely the same as that used in the Dutch disability weights study (18). In brief, we recruited medical doctors assumed to have sufficient knowledge of the
consequences of a broad range of diseases. A convenience sample of 75 doctors was contacted by postal questionnaire; 55 of these doctors had previously participated in similar studies (18, 19).
We replicated the Dutch disability weights study’s inter- polation procedure in which respondents were asked to place (or interpolate) disease stages on a disability scale. This scale ranged from 0 (worst imaginable health state) to 100 (best imaginable health state) and was formally calibrated in the ear- lier study with person trade-off derived disability weights for 16 conditions. We replaced the conditions “mild major depression” and “severe vision disorder” on the original scale with disorders that had comparable disability weights (mild to moderate panic disorder and grade 3–4 arthritis).
The duration of a disease stage to be valued was defined as one year for all diseases.
Analyses of the interpolation data For each disease-stage, we calculated the disability weight as: 1 – mean value/100. We examined the validity and reliability of the valuations by checking compliance with a pre-imposed order of stages of mental disorders (mild, moderate, severe); inspecting the Spearman rank correlation among respondents; and estimating the proportion of total variance that was at- tributable to the disease stages, using generalizability theory (G-study) (20, 21).
We also studied associations of age, sex, current profes- sion (GP, psychiatrist, researcher, other) and having medical experience (< 1 year versus > 1 year) with the valuations in a regression analysis. All analyses were performed in SAS ver- sion 6.12 (22).
Comparison with the Dutch disability weights study We compared disability weights for stages of major depression from the present study with those from the earlier study (18). In this study mild and severe depression were valued separately.
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Because respondents to the two studies were not drawn from independent studies, standard statistical testing was not used. Instead, we compared the 95% confidence intervals. The disability weights for obsessive–compulsive disorder and oesophageal cancer from both studies were compared to estimate test–retest reliability.
Overall disability weight We calculated an overall disability weight for major depression by combining the disability weights for each of the three classes of severity with their proportional prevalence. Prevalence data for the three classes were obtained from the NEMESIS study. We distributed proportionally the residual prevalence of cases with “unspecified severity” across the classes, excluding the class severe depression with psychotic features because we assumed psychotic features were unlikely to be missed.
Comparison with previous estimates We compared the overall disability weight from the present study with overall disability weights from four studies: the Dutch national burden of disease calculation for 1994 (3), the 1990 global burden of disease study (1), the Australian Burden of Disease Study (2), and another Australian study by Andrews et al. (23, 24). Both the Dutch and Australian Burden of Dis- ease studies used the same severity-specific disability weights from the Dutch disability weights study (18) to calculate an overall disability weight, but they used different methods to obtain proportional distributions of the classes of severity.
Results Description of classes of severity The lay texts and functional health status descriptions for the three classes of severity of major depression are shown in Table 1 (web version only, available at: http://www.who.int/bulletin).
Respondents A total of 49 medical doctors participated (24 men, 25 women; 65% response rate). Respondents had a mean age of 46.6 years (standard deviation = 8.8). On average respondents had 12.2 years of medical experience. A total of 53% of respondents were involved directly in patient care (14 general practitioners, 5 psychiatrists and 7 in other types of care); 35% worked in medical research and 12% worked in other health-related pro- fessions or were retired.
Analyses Table 2 and Table 3 show the disability weights with their 95% confidence intervals for the three severity classes of depression. All respondents but one complied with the ranking implied by the severity-specific classes of psychiatric disorders (mild, moderate to severe, severe depression with psychotic features). Respondents largely agreed with each other on the ranking of the 18 disease stages: the mean Spearman correlation coefficient was 0.83.
In the generalizability study, 76% of total variance was ex- plained by the disease stages. Respondents contributed another 6%, while a residual 18% remained unexplained. Regression analyses showed that the variables age, sex, current profession, and not having practical medical experience could not signifi- cantly predict the disability weights of the 18 disease stages.
Comparison with the Dutch disability weights study
Table 2 also provides the disability weights for major depres- sion obtained in the earlier Dutch study. Disability weights in the present study fell within the range of the 95% confidence intervals from the earlier study, and for moderate to severe depression they fell between the 95% confidence intervals of the separately valued classes of severity. EuroQol descriptions in the present study were generally less severe.
Table 2 also shows the disability weights for obsessive– compulsive disorder and cancer of the oesophagus. Re-valuation of their stages in the present study resulted in average values that fell within the 95% confidence intervals of the disability weights from the earlier Dutch study, except in the case of severe obsessive–compulsive disorder (present study 0.76, 95% confidence interval (CI) = 0.71–0.82 versus earlier study 0.56, 95% CI = 0.38–0.74).
For depression, the differences between the disability weights in the earlier study and those in this study did not appear to be larger than those for the two identically described conditions. The new disability weights fell within the earlier study’s 95% confidence intervals, and the absolute differences in the disability weights between the two studies (0.01 and 0.05) were smaller than for the identically described diseases (between 0.01 to 0.20).
Overall disability weight Table 3 shows how we combined the disability weights for each stage of major depression with the prevalence distribution of depressive cases across the severity classes to come up with an overall disability weight of 0.46.
Comparison to previous estimates In Table 4 (web version only, available at: http://www.who. int/bulletin) we compare the overall disability weight for depression to that from other studies. The estimate from the present study is similar to that of the 1990 global burden of disease study (disability weight = 0.47) (1) and close to those from the two Australian studies (approximately 0.41 in both studies) (2, 22–24). However, it is 73% higher than the one used in the 1994 Dutch national burden of disease calculation (disability weight = 0.27) (3). The lower 1994 disability weight results from the use of different proportional prevalences of severity classes to calculate the overall disability weight. For the 1994 calculation these proportional prevalences were based on expert opinion, while in the present study data from NEMESIS were used. Experts estimated that 60% of cases had mild major depression, 30% had moderate disease, 9% had severe disease and 1% had severe disease with psychotic features; in the NEMESIS study only 27% of cases had mild major depression (Table 3). The lower overall disability weight in the 1994 study is not caused by different valuations: the disability weights for the separate severity classes were similar between the two studies.
Discussion We derived disability weights for major depression occurring in a community setting by using prevalence and disability data from the Dutch community-based survey known as NEMESIS. The overall disability weight for major depression was similar to or higher than that used in several burden of disease studies (1–3, 23). This indicates that disability weights used in previous calculations of the burden of depression were not too high.
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Table 3. Disability weight for severity classes of major depression and calculation of the average disability weight
Severity of depression EuroQol 5D+C5La % of prevalenceb Disability weight 95% CId
Mild 112222 26.7c 0.19 0.16–0.22 Moderate to severe 113333 61.9c 0.51 0.46–0.55 Severe with psychotic features 214444 11.4 0.84 0.80–0.88 Total 100 0.46
a The six digits in this column correspond to scores on the six dimensions of the EuroQol 5D+C5L scale. These dimensions are mobility, self-care, usual activities, pain/discomfort, anxiety/depression, and cognition. A score of 1 indicates that a person has no problems functioning in that dimension; a score of 2 indicates that a person has a few problems functioning; a score of 3 indicates that a person has some or moderate problems; a score of 4 indicates there are severe problems; and a score of 5 indicates there are very severe problems or an inability to function. b Prevalence data obtained from the Netherlands Mental Health Study and Incidence Survey (NEMESIS) (7, 14). c Prevalence includes major depression of unspecified severity. d CI = confidence interval.
The disability weights for the separate classes of severity of depression did not deviate greatly from the Dutch disability weights study (18). In that study, descriptions of functional health status (using EuroQol) were based on case definitions and expert opinion and were not tailored to the community setting. On average these descriptions were somewhat more severe than the ones in the present study (which were based on self-reported disability from NEMESIS), and we expected our disability weights for different stages of depression to be lower (i.e. indicating less disability) than in the earlier study. Never- theless, the differences between the disability weights in the two studies did not appear to be significant. Similar disability weights for different stages of major depression were also found in an Australian study (24). As has been suggested before (25), the health status descriptions in EuroQol may have only a small effect on valuation. Apparently the label provided (disease and severity class) is much more important to evaluators.
The overall disability weight (i.e. the combination of stage-specific disability weights and prevalence) from the pres- ent study was similar to that used in the 1990 global burden of disease study and two Australian studies (1, 2, 23). Thus there is no reason to suspect that the disability weights were overes- timated previously. Therefore, the high burden of depression estimated by the 1990 study and by several national studies does not appear to have been exaggerated by overestimation of disability weights.
On the contrary, the burden of depression seems to have been underestimated in the 1994 Dutch national burden of disease calculation (3): the disability weight in the present study was 73% higher than the weight used in the 1994 calculation. In the 1994 study experts estimated that a larger proportion of
people had mild depression than was observed in NEMESIS. These prevalence data on the distribution of disability associ- ated with major depression had a major impact on the overall disability weight (and burden). This shows the importance of using quantitative epidemiological information in burden of disease calculations. The calculation of the overall disability weight using the proportional distribution of the classes of severity enabled us to better tailor the disability weight to the community setting. It also pointed out the previous underes- timation of the burden of major depression in the Netherlands and the importance of the epidemiological data.
Conclusions Our study found no indication that previously estimated dis- ability weights were overestimates because they had not been tailored to the community setting. Our tailored disability weights were similar to those found in most other studies, including the global burden of disease study, and do not decrease the estimated burden of depression. These results reinforce the validity of previous high estimates of the burden of depression. This study additionally points out the importance of obtaining sound epidemiological data in burden of disease studies. O
Funding: This study was sponsored by the Netherlands Insti- tute of Health Sciences. Presentation of this paper at the 15th REVES (International Network on Health Expectancy and the Disability Process) Conference, 5–7 May 2003, in Guadalajara, Mexico, was sponsored by the Erasmus University Trustfund.
Competing interests: none declared.
Résumé
La charge de dépression a-t-elle été surestimée Objectif Examiner la possibilité d’attribuer la valeur élevée des estimations de la charge de dépression à une surestimation des coefficients de pondération servant au calcul des années d’incapacité (indiquant une degré plus grave d’incapacité). Méthodes Des coefficients de pondération destinés au calcul des années d’incapacité et adaptés aux données de prévalence ont été établis. Les données d’incapacité empiriques provenant d’une enquête néerlandaise en communauté ont servi à décrire trois classes de gravité de la dépression et leurs taux de prévalence.
Des évaluations des coefficients de pondération pour chacune des classes ont été obtenu auprès d’experts, ce qui a permis de déterminer le coefficient de pondération global pour le calcul des années d’incapacité associées à la dépression. Résultats Les évaluations établies par les experts étaient similaires à celles fournies par les études antérieures. Dans le cas de la dépression, le coefficient de pondération global pour le calcul des années d’incapacité présentait une valeur analogue à celle obtenue dans les autres études, à l’exception du Calcul de
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Resumen
¿Se ha sobrestimado la carga de depresión? Objetivo Investigar si las altas estimaciones de la carga de depresión podrían atribuirse a una sobrestimación de las ponderaciones de la discapacidad (que reflejarían una mayor gravedad de ésta). Métodos Desarrollamos ponderaciones de la discapacidad ajustadas a los datos de prevalencia. Se usaron los datos empíricos de discapacidad de una encuesta llevada a cabo en una comunidad holandesa para describir tres clases de gravedad de la depresión y su prevalencia proporcional. Obtuvimos valoraciones de los expertos para cada clase y calculamos el peso global de la discapacidad por depresión. Resultados Las valoraciones de los expertos fueron similares a las de estudios anteriores. El peso global de la discapacidad
correspondiente a la depresión fue similar al de otros estudios, exceptuando el del Cálculo de la Carga de Morbilidad de los Países Bajos de 1994, que superó en un 73%. El menor peso de la discapacidad obtenido en el estudio holandés de 1994 se debió a que los expertos sobrestimaron la proporción de casos leves de depresión (60%, frente al 27% observado en los datos empíricos usados en el presente trabajo). Conclusión Este estudio no ha detectado ningún indicio de que se haya sobrestimado la discapacidad asociada a la depresión. El ejemplo holandés muestra la importancia de ajustar las ponderaciones de la discapacidad a los datos epidemiológicos sobre la prevalencia.
la charge de morbidité au Pays-Bas de 1994, qui aboutissait à un chiffre inférieur de 73 %. Le coefficient de pondération plus faible de l’étude néerlandaise résultait d’une surestimation par les experts de la proportion de cas de dépression sans gravité (60 % contre 27 % d’après les données empiriques utilisées dans la présente étude).
Conclusion Cette étude n’a mis en évidence aucun élément indiquant une surestimation de l’incapacité liée à la dépression. L’exemple néerlandais montre l’importance d’une adaptation des coefficients pondéraux servant au calcul des années d’incapacité aux données épidémiologiques de prévalence.
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7. Bijl RV, Ravelli A, van Zessen G. Prevalence of psychiatric disorder in the general population: results of the Netherlands Mental Health Survey and Incidence Study (NEMESIS). Social Psychiatry and Psychiatric Epidemiology 1998;33:587-95. 8. Andrews G, Henderson S, Hall W. Prevalence, comorbidity, disability and service utilisation. Overview of the Australian National Mental Health Survey. British Journal of Psychiatry 2001;178:145-53. 9. Bijl RV, Ravelli A. Current and residual functional disability associated with psychopathology: findings from the Netherlands Mental Health Survey and Incidence Study (NEMESIS). Psychological Medicine 2000;30:657-8. 10. Broadhead WE, Blazer DG, George LK, Tse CK. Depression, disability days, and days lost from work in a prospective epidemiologic survey. JAMA 1990;264:2524-8. 11. Kessler RC, Zhao S, Blazer DG, Swartz M. Prevalence, correlates, and course of minor depression and major depression in the National Comorbidity Survey. Journal of Affective Disorders 1997;45:19-30. 12. Sprangers MA, de Regt EB, Andries F, van Agt HM, Bijl RV, de Boer JB, et al. Which chronic conditions are associated with better or poorer quality of life? Journal of Clinical Epidemiology 2000;53:895-907.
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13. Regier DA, Kaelber CT, Rae DS, Farmer ME, Knauper B, Kessler RC, et al. Limitations of diagnostic criteria and assessment instruments for mental disorders. Implications for research and policy. Archives of General Psychiatry 1998;55:109-15. 14. Kruijshaar ME, Hoeymans N, Bijl RV, Spijker J, Essink-Bot ML. Levels of disability in major depression: findings from the Netherlands Mental Health Survey and Incidence Study (NEMESIS). Journal of Affective Disorders 2003;77:53-64. 15. Janssen MF, Bonsel GJ. Should the EuroQol descriptive system be extended from three to five levels? A methodological strategy with an empirical pilot. In: International Society for Pharmacoeconomics and Outcome Research. Rotterdam: International Society for Pharmacoeconomics and Outcome Research; 2002. 16. Krabbe PFM, Stouthard MEA, Essink-Bot ML, Bonsel GJ. The effect of adding a cognitive dimension to the EuroQol multiattribute health-status classification system. Journal of Clinical Epidemiology 1999;52:293-301. 17. Ware JE. SF-36 Health Survey: manual and interpretation guide. Boston (MA): Nimrod Press; 1993. 18. Stouthard MEA, Essink-Bot ML, Bonsel GJ, on behalf of DDW Group. Disability weights for diseases in the Netherlands. European Journal of Public Health 2000;10:24-30.
19. Essink-Bot ML, Pereira J, Packer C, Schwarzinger M, Burstrom K. Cross- national comparability of burden of disease estimates: the European Disability Weights Project. Bulletin of the World Health Organization 2002;80:644-52. 20. Krabbe PFM, Essink-Bot ML, Bonsel GJ. The comparability and reliability of five health-state valuation methods. Social Science and Medicine 1997;45:1641-52. 21. Streiner DL, Norman GR. Generalizability theory. In: Health measurement scales: a practical guide to their development and use. 2nd ed. New York: Oxford University Press; 1995. p. 128-43. 22. SAS Institute. SAS/STAT user’s guide. Cary (NC): SAS Institute; 1990. 23. Andrews G, Sanderson K, Corry J, Lapsley HM. Using epidemiological data to model efficiency in reducing the burden of depression. Journal of Mental Health Policy and Economics 2000;3:175-86. 24. Sanderson K, Andrews G. Mental disorders and burden of disease: how was disability estimated and is it valid? Australian and New Zealand Journal of Psychiatry 2001;35:668-76 . 25. Salomon JA, Murray CJL. A multi-method approach to measuring health- state valuations. Health Economics 2004;13:281-90.
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Table 1. Three severity classes (stages) of major depression used in this study
EuroQol 5D+C5L dimensionb
Severity Lay descriptiona Mobility Self- Usual Pain/ Anxiety/ Cognition care activities discomfort depression
Mild These people experience one or more 1 1 2 2 2 2 depressive episodes within a year. During these periods they have permanent feelings of sadness or emptiness or a permanent loss of interest or pleasure in nearly all activities. They may have problems eating or sleeping and can feel worthless or guilty. They may have thoughts of death.
Moderate These people experience one or more 1 1 3 3 3 3 to severe depressive episodes within a year. During these periods they have permanent feelings of sadness or emptiness and a permanent loss of interest or pleasure in nearly all activities. They have problems eating and/or sleeping and feel worthless or guilty. They may have thoughts of death.
Severe These people experience one or more 2 1 4 4 4 4 with depressive episodes within a year. During psychotic these periods they have permanent feelings features of sadness or emptiness and a permanent loss of interest or pleasure in nearly all activities. Furthermore, they experience delusions and hallucinations. They have problems eating and sleeping and feel worthless or guilty. They have thoughts of death.
a Descriptions are translated from Dutch. Lay descriptions were based on DSM-III-R criteria for major depression and severity. b The six digits in this column correspond to scores on the six dimensions of the EuroQol 5D+C scale. On the EuroQol 5D+C5L scale a score of 1 indicates that a person has no problems functioning; a score of 2 indicates that a person has a few problems functioning; a score of 3 indicates that a person has some or moderate problems; a score of 4 indicates there are severe problems; and a score of 5 indicates there are very severe problems or an inability to function. EuroQol scores were based on disability indicators from Dutch population surveys (7, 14).
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Table 2. Disability weights obtained in the present study compared with those obtained in the Dutch disability weights study (18)
Current study Dutch disability weights study
Disease and stage EuroQol Disability 95% CIc EuroQol Disability 95% CI scorea, b weight scorea weight
Major depression Mild 112222 0.19 0.16–0.22 113131 0.14 0.09–0.19 Moderate to severe 113333 0.51 0.46–0.55 Moderate 133133 0.35 0.27–0.42 Severe 335353 0.76 0.56–0.97 Severe with psychotic features 214444 0.84 0.80–0.88 335355 0.83 0.75–0.92
Cancer of the oesophagus Diagnosis and primary therapy 112441 0.52 0.48–0.57 112441d 0.53 0.36–0.70 After intentionally curative primary therapy 113331 0.42 0.37–0.46 113331 0.38 0.25–0.51 Irradically removed/disseminated carcinoma 114451 0.82 0.79–0.84 114451d 0.73 0.61–0.86
Obsessive–compulsive disorder Mild to moderate 113133 0.30 0.26–0.33 113133 0.24 0.17–0.32 Severe 133155 0.76 0.71–0.82 133155 0.56 0.38–0.74
a The six digits in this column correspond to scores on the six dimensions of the EuroQol 5D+C5L scale. These dimensions are mobility, self-care, usual activities, pain/discomfort, anxiety/depression, and cognition. A score of 1 indicates that a person has no problems functioning in that dimension; a score of 2 indicates that a person has a few problems functioning; a score of 3 indicates that a person has some or moderate problems; a score of 4 indicates there are severe problems; and a score of 5 indicates there are very severe problems or an inability to function. b These EuroQol scores were based on disability indicators from Dutch population surveys (7, 14). c CI = confidence interval. d For these stages the Dutch disability weights study gave two EuroQol 5D+C3L descriptions, each having a 50% possibility of occurring. We re-coded these into EuroQol 5D+C5L levels by averaging the two descriptions, thereby using the two additional levels (level 2 and 4) of this system.
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Table 4. Comparison of overall disability weights for depression from different studies
Studya Method of deriving Severity classes Distribution Overall disability disability weight across classes weight
Present study Interpolation on a Mild; Dutch survey datab 0.459 (the Netherlands) person trade-off moderate to severe; calibrated disability scale severe with psychotic features
1990 global burden Person trade-off Treated versus Expert estimation 0.469 of disease study (1) Untreated (established market economies)
Dutch national burden Dutch disability weights Mild; Expert estimation 0.266 of disease calculation (3) study: person trade-off moderate; (the Netherlands) and interpolation on a severe; person trade-off severe with psychotic features calibrated disability scale
Australian Burden Dutch disability weights Mild; Short Form-12 health 0.41 (m) 0.37 (f) of Disease Study (2) study: person trade-off moderate; survey cut-off scores (Australia) and interpolation severe in Australian surveyc
Andrews et al. (23, 24) Person trade-off Mild episode; Short Form-12 cut-off 0.417 (Australia) moderate episode; scores in Australian severe episode surveyc
a Information in parentheses indicates where study took place. b Data were derived from the Netherlands Mental Health Study and Incidence Survey (NEMESIS) (7, 14). c Data collected during the Australian National Mental Health and Wellbeing Survey (8).